Maintaining a degree of moisture control is desirable for a variety of applications. For example, one application involves devices with electronic circuitry provided within some form of closed housing. The moisture within the closed housing (often caused by humidity) needs to be controlled in order to limit or avoid corrosion of metal within the circuitry or condensation of moisture on exposed circuit lines. Closed housings that are configured to prevent the permeation of moisture are called hermetic packages. Hermetic packaging also prevents the permeation of undesirable gases into the device.
As specific examples, hermetic packaging may be used to prevent humidity and gas permeation in electronic assemblies that contain Radio Frequency (RF) integrated circuits and Microelectromechanical systems (MEMS). MEMS are integrated micro devices or systems combining electrical and mechanical components. MEMS devices may be fabricated using standard integrated circuit batch processing techniques and may have a variety of applications including sensing, controlling, and actuating on the micro scale. MEMS devices may function individually or in arrays to generate effects on a macro scale.
Many RF integrated circuits and MEMS devices benefit from a hermetic environment in order to obtain maximum performance. The hermetic package also provides protection and an optimal operating environment for the devices. However, it is very difficult and very expensive to package such devices.
The I/O connections are the critical areas for hermetic wafer level packaging. For RF connections, the I/O connections must not only be hermetic but must provide the necessary impedance to minimize reflections between the inside of the package and the outside. Typically, these I/O connections are made on the circuit side of the carrier by running insulated leads under or through the hermetic seal. The length of these leads and their electrical interaction with the seal material can significantly degrade the electrical performance. In addition, these connections must be thermally matched to the package materials to assure the package will be hermetic at the operating temperature.